1. Field of the Invention
The present invention relates to an ink jet print apparatus, and an ink jet printing method. More particularly, the present invention relates to an ink jet print apparatus, an ink jet printing method, program controlling the apparatus, and a storage medium storing the program that allow a reduction in uneven colors due to the difference in recording time between recording black inks and color inks, the time difference being caused by performing printing by bidirectional scanning of recording heads.
2. Description of the Related Art
In ink jet type print apparatuses, when performing color printing on a commonly-used print medium such as plain paper, it has been difficult to achieve an improvement in recording speed and an enhancement of image quality.
Methods for improving the recording speed that have been used include a method where the size of the region recordable by one scan is increased by lengthening the recording head; a method where the recording (driving) frequency of recording heads is increased; and a method where the printing is performed by bidirectional scanning of the recording heads. Among these methods, the xe2x80x9cbidirectional printingxe2x80x9d method is a cost-effective method as a total system, since the energy required for obtaining a given throughput is dispersed over time, as compared to the case where printing is performed by unidirectional scanning, i.e., unidirectional printing.
When performing such bidirectional printing, the discharge order of black ink and color inks constituting a pixel differs between the advance and return scanning directions of the recording heads. This is because the discharge ports (hereinafter referred to as nozzles) for the black ink and color inks are arranged in the scanning direction, and the discharging order for the black ink and color inks determined by this arranging manner is different between the advance direction and the return direction. When the discharge order of black ink and color inks is different, a difference in the hue can occur between the region recorded in the advance direction scanning and the region recorded by the return direction scanning, thereby causing degradation in the image quality. For example, band-like uneven colors may occur over an entire printed color image, which causes the poor image quality. As coutermeasures against this, for example, Japanese Patent Application Publication No. 11-313790 proposes a method for eliminating the above-described uneven colors by configuring a head where rows of nozzles of black ink and color inks are disposed symmetrically with respect to the scanning direction thereof.
On the other hand, the present invention uses a high image quality when printing a text and the like on plain paper, an ink jet print device using a pigment-based black ink is being provided. This arrangement especially allows black letters to be improved in quality and density.
In this arrangement, such a pigment-based black ink is frequently provided with a composition that is relatively impermeable with respect to paper in order to prevent ink from permeating along fabrics of paper. Such an arrangement is referred to as feathering. Also, recording heads are frequently used that have a configuration where black ink nozzles and color ink nozzles are arranged in a direction substantially perpendicular to the scanning direction of the recording heads. In the case of the configuration where the nozzles discharging a black ink, which has a low permeability, and the nozzles discharging color inks, which have a high permeability such as to exhibit a permeability value higher than a predetermined value (hereinafter, ink with a high permeability is referred to as a xe2x80x9csuper-permeable inkxe2x80x9d) are arranged along the scanning direction (such an arrangement is referred to as a lateral nozzle-arrangement), an imparting time difference between a black ink and color inks is small since the black ink and color inks are imparted to the same scanning region during one scan when printing is performed on a predetermined region. As a result, for example, when printing a black shade pattern on a print region with a yellow color, bleeding occurs at a boundary portion of the region where printing is performed with a black ink and the region where printing is performed with color inks, or when printing a pattern where a high-density black patch is fringed with a yellow color, a so-called white haze phenomenon can occur, which indicates a reduction in the density due to the retreat of the ink with a low permeability. In order to reduce the above-described bleeding and white haze, recording heads where black nozzles and color nozzles are arranged to be offset along a direction perpendicular to the scanning direction (such an arrangement is referred to as a longitudinal nozzle-arrangement) are frequently used.
However, when colors where a black ink dot and color ink dots are intermingled, such as a gray color, are to be printed by bidirectional printing using the recording heads with the above-described longitudinal nozzle-arrangement, the discharge times between the black ink and the color inks are different, at the right and left ends in each scanning region. This raises a problem that, particularly at the above-described two ends, even if the color is a given gray, a difference in the hue will occur in each scanning region (hereinafter referred to as band). Consequently, a streak-like uneven color can occur for each band over the entire paper on which the printing is performed.
In the above-described longitudinal nozzle-arrangement, during scanning of the recording head, respective scanning regions to which black ink nozzles and color ink nozzles correspond, are different from each other. Therefore, the black ink nozzle corresponds to a predetermined scanning region during an earlier scanning (a first scanning), and the color ink nozzle corresponds to the predetermined scanning region during a later scanning (a second scanning), or conversely, the color ink nozzle corresponds to the predetermined scanning region during an earlier scanning (the first scanning), and the black ink nozzle corresponds to the predetermined scanning region during a later scanning (the second scanning). Consider, for example, a case where the black ink nozzle corresponds to the predetermined scanning region during the first scanning in the advance direction (e.g., a scanning from the left to the right), and the color ink nozzle corresponds to the predetermined scanning region during the second scanning in the return direction (e.g., a scanning from the right to the left). In this case, with respect to the right end of the above-described predetermined scanning region, the black ink is discharged at the end of the first scanning in the advance direction, and the color ink is discharged at the beginning of the second scanning in the return direction, the second scanning being performed immediately after the first scanning. As a consequence, the discharge time difference between the black ink and each of the color inks becomes small. On the other hand, with respect to the left end of the above-described predetermined scanning region, the black ink is discharged at the beginning of the first scanning in the advance direction, and the color ink is discharged at the end of the second scanning in the return direction, the second scanning being performed immediately after the first scanning. As a result, the discharge time difference between black and color inks becomes large. That is, when performing bidirectional printing using the head with the above-described longitudinal nozzle-arrangement, there occur a portion where the black ink is discharged by the black ink nozzle at the end of the scanning and where, upon the change of scanning direction immediately after the above-described discharging, the color ink is discharged from the color ink nozzle, and a portion where the black ink is discharged by the black ink nozzle at the beginning of the scanning and where, after about one round trip of the above-described scanning, the color ink is discharged from the color ink nozzle, thereby producing the above-described time difference.
For example, when a black ink with a low permeability is earlier discharged and thereafter super-permeable color inks are discharged, the black ink is pressed into the paper and the density thereof decreases, since the color inks are dotted before the black ink has been dotted and permeated through the paper. Therefore, even if, at the right end and the left end of the paper, printing is performed by the same order and the same discharge amount, a density difference will be caused by the above-described time difference. If the density difference by the time difference occurs in one band, the density difference will be difficult to be visually recognized since the degree of density difference gradually changes along the scanning direction of the recording head. However, if the density difference continuously occurs in several bands over the entire paper, the largeness and smallness of the above-described time difference will be repeated for each band particularly at the left and right ends, and the density difference between the bands will become visually noticeable, thereby causing a degradation in the image quality.
Accordingly, it is an object of the present invention to solve the above-described conventional problems and to provide an ink jet print apparatus, printing method, program controlling the apparatus, and a storage medium storing the program that allows high image-quality printing to be realized without a significant reduction in overall printing speed, by judging the probability of occurrence of uneven color due to the above-described time difference, and by selectively using the bidirectional printing and unidirectional printing based on the above-mentioned judgement.
In order to achieve the above-described object, the present invention provides an ink jet print apparatus capable of a bidirectional printing mode where printing is performed on a print medium by both a main scan in an advance direction and a main scan in a return direction of print heads for discharging a plurality of different kinds of inks, and capable of a unidirectional printing mode where printing is performed on the print medium by either the main scan in the advance direction or the main scan in the return direction of the print heads. This apparatus comprises acquiring means that, based on print data corresponding to a predetermined region on the printing medium, acquires information of respective ink amounts to be imparted to the predetermined region for the plurality of different kinds of inks; determining means that, based on the above-described information acquired by the acquiring means, determines whether the respective imparting amounts of the plurality of different kinds of inks exceed respective predetermined amounts that have been predetermined corresponding to the respective inks. Herein, (a) when the determining means determines that the respective imparting amounts of all of the plurality of different kinds of inks exceed the respective predetermined amounts, printing with respect to the predetermined region is performed in the unidirectional print mode; and (b) when the determining means determines that at least one of the respective imparting amounts of the plurality of different kinds of inks does not exceed the predetermined amount thereof, printing with respect to the predetermined region is performed in the bidirectional print mode.
Also, the present invention provides an ink jet printing method where printing is performed in any one of a bidirectional printing mode in which printing is performed on a print medium by both a main scan in an advance direction and that in a return direction of print heads for discharging a plurality of different kinds of inks, and a unidirectional printing mode in which printing is performed on the print medium by one of the main scan in the advance direction and the main scan in the return direction of the print heads. This method comprising the step of acquiring, based on print data corresponding to the predetermined region on the print medium, information of respective ink amounts to be imparted to the predetermined region for the plurality of different kinds of inks; and the step of determining, based on the information acquired by the above-described acquiring means, whether the respective imparting amounts of the plurality of different kinds of inks exceed respective predetermined amounts that have been predetermined corresponding to the respective inks. In this determining step, (a) when it is determined that the respective imparting amounts of all of the plurality of different kinds of inks exceed the respective predetermined amounts, printing with respect to the predetermined region is performed in the unidirectional print mode; and (b) when it is determined that the determining means determines that at least one of the respective imparting amounts of the plurality of different kinds of inks does not exceed the predetermined amount thereof, printing with respect to the predetermined region is performed in the bidirectional print mode.
Furthermore, the present invention provides a control program for controlling an ink jet print apparatus that performs printing on a print medium using print heads for discharging a plurality of different kinds of inks. This program comprises the step of acquiring, based on print data corresponding to the predetermined region on the print medium, information of respective ink amounts to be imparted to the predetermined region for the plurality of different kinds of inks; the step of determining, based on the above-described information acquired by the acquiring means, whether the respective imparting amounts of the plurality of different kinds of inks exceed respective predetermined amounts that have been predetermined corresponding to the respective inks. In the determining step, (a) when it is determined that the respective imparting amounts of all of the plurality of different kinds of inks exceed the respective predetermined amounts, a unidirectional print mode where printing is performed by any one of a main scan in an advance direction and that in a return direction of the print heads, is selected, and (b) when it is determined that at least one of the respective imparting amounts of the plurality of different kinds of inks does not exceed the predetermined amount thereof, a bidirectional print mode where printing is performed by both the main scan in the advance direction and that in the return direction of the print heads, is selected.
Moreover, the present invention provides a computer-readable storage medium that stores the above-described control program.
Also, the present invention provides an ink jet printing method where printing is performed in any one of a bidirectional printing mode where printing is performed on a print medium by both a main scan in an advance direction and that in a return direction of print heads for discharging a plurality of different kinds of inks, and a bidirectional printing mode where printing is performed on the print medium by one of the main scan in the advance direction and that in the return direction of the print heads. This method comprises the step of acquiring, based on print data corresponding to the predetermined region on the print medium, information of the respective ink amounts to be imparted to a predetermined region for the plurality of different kinds of inks; and the step of determining, based on the information acquired by the acquiring means, whether the respective imparting amounts of the plurality of different kinds of inks exceed respective predetermined amounts that have been predetermined corresponding to the respective inks; and the step of switching a print mode to be used from the bidirectional print mode to the unidirectional one when, in the determining step, it is determined that the respective imparting amounts of the plurality of different kinds of inks exceed the respective predetermined amounts.
With these arrangements, for predetermined regions where different kinds of inks are discharged, when the respective imparting amounts of the plurality of different kinds of inks exceed the respective predetermined amounts, printing with respect to the predetermined region is performed in the unidirectional print mode (print by one of the advance scanning and the return scanning) instead of performing in the bidirectional print mode (print by both the advance scanning and the return scanning). Thereby, with regard to the above-described different kinds of inks, printing by using ink imparting amounts exceeding the above-described predetermined amount can be prevented from being performed by the bidirectional scanning. This allows uneven colors (uneven densities) caused by discharge time difference, which would occur in a bidirectional printing, to be eliminated.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.